Frost Heave And Deck Footing
When a deck heaves it appears that it is sinking on a portion of the deck when in fact it is raising somewhere else. Heave is cause when foundations are not deeper than ice that has formed in the ground during winter months. The ground does not have to be saturated with water to freeze. Most soils retain water and in the Midwest this is a common occurrence. Frost penetration varies in different parts of the country.
Northern IL and southern WI the frost level is between 42” and 48” depending how far north you are. If a foundation pier is less than the frost level, moisture collected under the pier will freeze and expand forcing the pier upwards. People find it hard to believe that a little ice can do that kind of damage but year after year as more and more water collects under the pier, the pier will heave more and more. It is a fairly common problem with improperly built decks.
Unless you probe the pier there is no real way of determining how deep it is, but you can bet if it is heaving it is not below the frost line and should be replaced.
Unfortunately, the damage to the deck will already have occurred forcing you to replace an entire section or the entire deck.
When engaging a contractor to build a new deck be sure they get a permit and comply with the local building codes or the International Residential Code and be sure they are aware of local frost levels to avoid this common problem.
OnDeck is a 30-year-old deck builder serving Lake and Cook Counties. Contact OnDeck today for all your deck related needs.